This invention relates to a method for detecting the presence of undesired matter in an egg as described in the preamble of claim 1. Such a method is generally known in practice and is based on the principle of color spectrum photometry. Although the present invention is generally applicable for detecting undesired matter in general, the present invention is of interest in particular for detecting the presence of blood in eggs, for which reason the present invention will be described hereinbelow for such an exemplary application.
In practice, it may happen that an egg intended for consumption, for instance a chicken egg, contains blood. Although the presence of blood is, in principle, harmless, the consumer generally does not find the presence of blood a pleasant sight. For this reason, egg-processing companies generally entertain the desire to supply xe2x80x9cpurexe2x80x9d eggs only, that is, eggs with as little undesired matter, such as blood, as possible. This implies there is a need for detection equipment to determine whether blood is present in an egg. Such detection equipment is coupled to sorting equipment to remove, during the sorting and packing of eggs, the unsuitable eggs, that is, the eggs that contain undesired matter such as blood.
Naturally, such detection equipment should be non-destructive. A well-proven detection method for detecting the presence of blood relies on the fact that an egg is semi-transparent, and is based on the absorption characteristics of eggs and blood. Blood has a strong absorption line at 577 nm; a normal egg has a much lower absorption at this wavelength, and the absorption characteristic of a normal egg is virtually flat in this wavelength range. By directing light at an egg and measuring the amount of transmitted light at 577 nm, the presence of blood can in principle be determined. However, the light, when passing through the egg, will be considerably weakened by the egg itself, and the extent of weakening can vary from one egg to another: it depends inter alia on the thickness of the egg. To correct for the extent of absorption/weakening by the egg itself, the amount of transmitted light is also measured in a narrow wavelength band at some distance from the absorption line referred to; in practice, a wavelength distance of 20 nm is used, and this reference measurement is carried out at approximately 597 nm. The result of the measurement at 577 nm can be corrected for the result of the measurement at 597 nm, to thereby obtain a measuring signal that depends substantially exclusively on the absorption by blood.
In practice, this method has proven to yield good results. Even eggs that contain only minute amounts of blood can be detected with a high probability, while the probability that a bloodless egg is falsely rejected is particularly low.
The good results referred to, however, have so far applied to white eggs only. In colored eggs, the results are less good, because the coloring of the shell plays a role. In particular, the measuring method referred to has been found to be less reliable in brown eggs. The reason for this reduced reliability has been found to reside in the fact that the shell of brown eggs itself exhibits an absorption in the range of 577 nm. This makes it difficult to discriminate between absorption caused by blood and absorption caused by the brown shell.
It is therefore an object of the present invention to make the known blood detection method suitable for examining brown eggs as well.
In particular, the object of the present invention is to provide a relatively simple method which enables determining the presence of blood in brown eggs with great accuracy.
More particularly, the object of the present invention is to provide a method for processing the measuring signals that are provided by a standard detection device, without requiring modification of such a standard detection device.
To that end, the method according to the invention has the features as described in the characterizing clause of claim 1.